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  • Java Executor: Small tasks or big ones?

    - by Arash Shahkar
    Consider one big task which could be broken into hundreds of small, independently-runnable tasks. To be more specific, each small task is to send a light network request and decide upon the answer received from the server. These small tasks are not expected to take longer than a second, and involve a few servers in total. I have in mind two approaches to implement this using the Executor framework, and I want to know which one's better and why. Create a few, say 5 to 10 tasks each involving doing a bunch of send and receives. Create a single task (Callable or Runnable) for each send & receive and schedule all of them (hundreds) to be run by the executor. I'm sorry if my question shows that I'm lazy to test these and see for myself what's better (at least performance-wise). My question, while looking after an answer to this specific case, has a more general aspect. In situations like these when you want to use an executor to do all the scheduling and other stuff, is it better to create lots of small tasks or to group those into a less number of bigger tasks?

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  • Need some help understanding this problem

    - by Legend
    I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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  • Endianness and C API's: Specifically OpenSSL.

    - by Hassan Syed
    I have an algorithm that uses the following OpenSSL calls: HMAC_update() / HMAC_final() // ripe160 EVP_CipherUpdate() / EVP_CipherFinal() // cbc_blowfish These algorithm take a unsigned char * into the "plain text". My input data is comes from a C++ std::string::c_str() which originate from a protocol buffer object as a encoded UTF-8 string. UTF-8 strings are meant to be endian neutrial. However I'm a bit paranoid about how OpenSSL may perform operations on the data. My understanding is that encryption algorithms work on 8-bit blocks of data, and if a unsigned char * is used for pointer arithmetic when the operations are performed the algorithms should be endian neutral and I do not need to worry about anything. My uncertainty is compounded by the fact that I am working on a little-endian machine and have never done any real cross-architecture programming. My beliefs/reasoning are/is based on the following two properties std::string (not wstring) internally uses a 8-bit ptr and a the resulting c_str() ptr will itterate the same way regardless of the CPU architecture. Encryption algorithms are either by design, or by implementation, endian neutral. I know the best way to get a definitive answer is to use QEMU and do some cross-platform unit tests (which I plan to do). My question is a request for comments on my reasoning, and perhaps will assist other programmers when faced with similar problems.

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  • Async WebRequest Timeout Windows Phone 7

    - by Tyler
    Hi All, I'm wondering what the "right" way of timing out an HttpWebRequest is on Windows Phone7? I've been reading about ThreadPool.RegisterWaitForSingleObject() but this can't be used as WaitHandles throw a Not implemented exception at run time. I've also been looking at ManualReset events but A) Don't understand them properly and B) Don't understand how blocking the calling thread is an acceptable way to implement a time out on an Async request. Here's my existing code sans timeout, can someone please show me how I would add a timeout to this? public static void Get(Uri requestUri, HttpResponseReceived httpResponseReceivedCallback, ICredentials credentials, object userState, bool getResponseAsString = true, bool getResponseAsBytes = false) { var httpWebRequest = (HttpWebRequest)WebRequest.Create(requestUri); httpWebRequest.Method = "GET"; httpWebRequest.Credentials = credentials; var httpClientRequestState = new JsonHttpClientRequestState(null, userState, httpResponseReceivedCallback, httpWebRequest, getResponseAsString, getResponseAsBytes); httpWebRequest.BeginGetResponse(ResponseReceived, httpClientRequestState); } private static void ResponseReceived(IAsyncResult asyncResult) { var httpClientRequestState = asyncResult.AsyncState as JsonHttpClientRequestState; Debug.Assert(httpClientRequestState != null, "httpClientRequestState cannot be null. Fatal error."); try { var webResponse = (HttpWebResponse)httpClientRequestState.HttpWebRequest.EndGetResponse(asyncResult); } }

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  • Is is possible to determine a password input string as plaintext or hashed?

    - by Godders
    I have a RESTful API containing a URI of /UserService/Register. /UserService/Register takes an XML request such as: <UserRegistrationRequest> <Password>password</Password> <Profile> <User> <UserName>username</UserName> </User> </Profile> </UserRegistrationRequest> I have the following questions given the above scenario: Is there a way (using C# and .Net 3.5+) of enforcing/validating that clients calling Register are passing a hashed password rather than plaintext? Is leaving the choice of hashing algorithm to be used to the client a good idea? We could provide a second URI of /UserService/ComputePasswordHash which the client would call before calling /UserService/Register. This has the benefit of ensuring that each password is hashed using the same algorithm. Is there a mechanism within REST to ensure that a client has called one URI before calling another? Hope I've explained myself ok. Many thanks in advance for any help.

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  • Efficiently Serving Dynamic Content in Google App Engine

    - by awegawef
    My app on google app engine returns content items (just text) and comments on them. It works like this (pseudo-ish code): query: get keys of latest content #query to datastore for each item in content if item_dict in memcache: use item_dict else: build_item_dict(item) #by fetching from datastore store item_dict in memcache send all item_dicts to template Sorry if the code isn't understandable. I get all of the content dictionaries and send them to the template, which uses them to create the webpage. My problem is that if the memcache has expired, for each item I want to display, I have to (1) lookup item in memcache, (2) since no memcache exists I must fetch item from the datastore, and (3) store the item in memcache. These calls build up quickly. I don't set an expire time for the entries to the memcache, so this really only happens once in the morning, but the webpage takes long enough to load (~1 sec) that the browser reports it as not existing. Regularly, my webpages take about 50ms to load. This approach works decently for frequent visits, but it has its flaws as shown above. How can I remedy this? The entries are dynamic enough that I don't think it would be in my best interest to cache my initial request. Thanks in advance

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  • When is a method eligible to be inlined by the CLR?

    - by Ani
    I've observed a lot of "stack-introspective" code in applications, which often implicitly rely on their containing methods not being inlined for their correctness. Such methods commonly involve calls to: MethodBase.GetCurrentMethod Assembly.GetCallingAssembly Assembly.GetExecutingAssembly Now, I find the information surrounding these methods to be very confusing. I've heard that the run-time will not inline a method that calls GetCurrentMethod, but I can't find any documentation to that effect. I've seen posts on StackOverflow on several occasions, such as this one, indicating the CLR does not inline cross-assembly calls, but the GetCallingAssembly documentation strongly indicates otherwise. There's also the much-maligned [MethodImpl(MethodImpOptions.NoInlining)], but I am unsure if the CLR considers this to be a "request" or a "command." Note that I am asking about inlining eligibility from the standpoint of contract, not about when current implementations of the JITter decline to consider methods because of implementation difficulties, or about when the JITter finally ends up choosing to inline an eligible method after assessing the trade-offs. I have read this and this, but they seem to be more focused on the last two points (there are passing mentions of MethodImpOptions.NoInlining and "exotic IL instructions", but these seem to be presented as heuristics rather than as obligations). When is the CLR allowed to inline?

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  • Why Firebug pretends that my stylesheet is calling my xmlrpc ?

    - by Rebol Tutorial
    Firebug shows a request which causes a huge delay to http://reboltutorial.com/wp-content/themes/minaflow/none Details below but I don't understand why it says it comes from xmlrpc and the stylesheet: Date Sun, 04 Apr 2010 16:10:02 GMT Server Apache X-Powered-By PHP/5.2.13 X-Pingback http://reboltutorial.com/xmlrpc.php Expires Wed, 11 Jan 1984 05:00:00 GMT Cache-Control no-cache, must-revalidate, max-age=0 Pragma no-cache Set-Cookie wordpress_test_cookie=WP+Cookie+check; path=/; domain=.reboltutorial.com Last-Modified Sun, 04 Apr 2010 16:10:03 GMT Vary Accept-Encoding Content-Encoding gzip Keep-Alive timeout=2, max=94 Connection Keep-Alive Transfer-Encoding chunked Content-Type text/html; charset=UTF-8 Requêtemise en page impression GET /wp-content/themes/minaflow/none HTTP/1.1 Host: reboltutorial.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; fr; rv:1.9.2) Gecko/20100115 Firefox/3.6 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Connection: keep-alive Referer: http://reboltutorial.com/wp-content/themes/minaflow/style.css Cookie: _csoot=1267966575980; _csuid=4b6f27395991a2ff; wp-settings-1=editor%3Dhtml%26align%3Dleft%26m0%3Do%26m1%3Do%26m2%3Do%26m3%3Dc%26m4%3Do%26m5%3Dc%26m6%3Do%26m7%3Do%26m8%3Dc%26m9%3Dc%26m10%3Dc%26m11%3Do%26m12%3Dc%26m13%3Dc%26m14%3Dc%26m15%3Dc; wp-settings-time-1=1270384700; subscribe_checkbox_=unchecked; PHPSESSID=o70hjpjf7uj2hb4doe4k0o5co5; wordpress_test_cookie=WP+Cookie+check; xumgeqhxmhohxipF=Erjixxeeskfgnlba; SJECT=CKON; wordpress_=admin%7C1271592539%7C392c555d9051c6fa184074d8441cc472; wordpress_logged_in_=admin%7C1271592539%7C0e7a92bda53cc2f5afc32962237a1037; rcBDvgtspmuEsyzp=rmqjtFbCfheGCjBw; prli_click_15=creatingstandard; prli_visitor=m7928r

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  • Facebook android app keeps crashing even though there are no errors in my code. Why?

    - by user1554479
    If you import the facebook SDK library, the code works (ignore the deprecated methods for now lol) and there are no errors or warnings. However, when I run my facebook app on my Android 2.2 or 4.2 emulator, the app crashes either upon opening or after the log on screen. Why? Is it because I'm not implementing Async Task? If so, how does that work? Here's my code: package com.sara.facebookappl; import java.io.IOException; import java.net.MalformedURLException; import java.net.URL; import org.json.JSONException; import org.json.JSONObject; import android.app.Activity; import android.content.Intent; import android.content.SharedPreferences; import android.content.SharedPreferences.Editor; import android.os.Bundle; import android.os.StrictMode; import android.view.Menu; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.ImageView; import android.widget.TextView; import android.widget.Toast; import com.facebook.android.DialogError; import com.facebook.android.Facebook; import com.facebook.android.Facebook.DialogListener; import com.facebook.android.FacebookError; import com.facebook.android.Util; public class MainActivity extends Activity implements OnClickListener, DialogListener { Facebook fb; ImageView button; SharedPreferences sp; TextView welcome; Button post; @SuppressWarnings("deprecation") @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); post=(Button)findViewById(R.id.button1); String APP_ID = getString(R.string.APP_ID); fb= new Facebook(APP_ID); sp =getPreferences(MODE_PRIVATE); String access_token=sp.getString("access_token", null); long expires=sp.getLong("access_expires", 0); if (access_token !=null) { fb.setAccessToken(access_token); } if(expires !=0) { fb.setAccessExpires(expires); } button=(ImageView)findViewById(R.id.login); button.setOnClickListener((OnClickListener) this); updateButtonImage(); } @SuppressWarnings("deprecation") private void updateButtonImage() { // TODO Auto-generated method stub post.setVisibility(Button.VISIBLE); button.setImageResource(R.drawable.com_facebook_loginbutton_blue); //logout button if (fb.isSessionValid()) { button.setImageResource(R.drawable.com_facebook_loginbutton_blue); // ^logout button JSONObject obj=null; URL img_url =null; try { String jsonUser= fb.request("me"); obj = Util.parseJson(jsonUser); String id=obj.optString("id"); String name = obj.optString("name"); welcome.setText("Welcome, " + name); }catch(FacebookError e) { e.printStackTrace(); }catch (JSONException e) { e.printStackTrace(); }catch (MalformedURLException e) { e.printStackTrace(); }catch (IOException e) { e.printStackTrace(); } }else { post.setVisibility(Button.VISIBLE); button.setImageResource(R.drawable.com_facebook_loginbutton_blue); } } @SuppressWarnings("deprecation") public void buttonClicks(View v) { switch (v.getId()) { case R.id.button1: //post Bundle params= new Bundle(); params.putString("name", "User X"); params.putString("caption", "Rating"); params.putString("description", "User X Rated"); params.putString("link", "http://..."); fb.dialog(MainActivity.this, "feed", params, new Facebook.DialogListener() { @Override public void onFacebookError(FacebookError e) { // TODO Auto-generated method stub } @Override public void onError(DialogError e) { // TODO Auto-generated method stub } @Override public void onComplete(Bundle values) { // TODO Auto-generated method stub } @Override public void onCancel() { // TODO Auto-generated method stub } }); break; } } @SuppressWarnings("deprecation") public void onClick(View v) { if(fb.isSessionValid()) { try { fb.logout(getApplicationContext()); updateButtonImage(); //button will close our our session }catch(MalformedURLException e) { e.printStackTrace(); } catch(IOException e) { e.printStackTrace(); } }else{ //login into facebook fb.authorize(MainActivity.this, new String[] {"email"}, new Facebook.DialogListener() { @Override public void onFacebookError(FacebookError e) { // TODO Auto-generated method stub Toast.makeText(MainActivity.this, "fbError", Toast.LENGTH_SHORT).show(); } @Override public void onError(DialogError e) { // TODO Auto-generated method stub Toast.makeText(MainActivity.this, "onError", Toast.LENGTH_SHORT).show(); } @Override public void onComplete(Bundle values) { // TODO Auto-generated method stub Editor editor=sp.edit(); editor.putString("access_token", fb.getAccessToken()); editor.putLong("access_expires", fb.getAccessExpires()); editor.commit(); updateButtonImage(); } @Override public void onCancel() { // TODO Auto-generated method stub Toast.makeText(MainActivity.this, "onCancel", Toast.LENGTH_SHORT).show(); } }); } } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.activity_main, menu); return true; } @SuppressWarnings("deprecation") @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); fb.authorizeCallback(requestCode, resultCode, data); } @Override public void onComplete(Bundle values) { // TODO Auto-generated method stub } @Override public void onFacebookError(FacebookError e) { // TODO Auto-generated method stub } @Override public void onError(DialogError e) { // TODO Auto-generated method stub } @Override public void onCancel() { // TODO Auto-generated method stub } } LogCat Errors: 12-16 04:56:59.070: E/AndroidRuntime(822): FATAL EXCEPTION: main 12-16 04:56:59.070: E/AndroidRuntime(822): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sara.facebookappl/com.sara.facebookappl.MainActivity}: android.os.NetworkOnMainThreadException 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.ActivityThread.access$600(ActivityThread.java:141) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.os.Handler.dispatchMessage(Handler.java:99) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.os.Looper.loop(Looper.java:137) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.ActivityThread.main(ActivityThread.java:5039) 12-16 04:56:59.070: E/AndroidRuntime(822): at java.lang.reflect.Method.invokeNative(Native Method) 12-16 04:56:59.070: E/AndroidRuntime(822): at java.lang.reflect.Method.invoke(Method.java:511) 12-16 04:56:59.070: E/AndroidRuntime(822): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 12-16 04:56:59.070: E/AndroidRuntime(822): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 12-16 04:56:59.070: E/AndroidRuntime(822): at dalvik.system.NativeStart.main(Native Method) 12-16 04:56:59.070: E/AndroidRuntime(822): Caused by: android.os.NetworkOnMainThreadException 12-16 04:56:59.070: E/AndroidRuntime(822): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117) 12-16 04:56:59.070: E/AndroidRuntime(822): at java.net.InetAddress.lookupHostByName(InetAddress.java:385) 12-16 04:56:59.070: E/AndroidRuntime(822): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236) 12-16 04:56:59.070: E/AndroidRuntime(822): at java.net.InetAddress.getAllByName(InetAddress.java:214) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpConnection.(HttpConnection.java:70) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpConnection.(HttpConnection.java:50) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:340) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:87) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpConnection.connect(HttpConnection.java:128) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:316) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.makeSslConnection(HttpsURLConnectionImpl.java:461) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.connect(HttpsURLConnectionImpl.java:433) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:290) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:240) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:282) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:177) 12-16 04:56:59.070: E/AndroidRuntime(822): at libcore.net.http.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:271) 12-16 04:56:59.070: E/AndroidRuntime(822): at com.facebook.android.Util.openUrl(Util.java:219) 12-16 04:56:59.070: E/AndroidRuntime(822): at com.facebook.android.Facebook.requestImpl(Facebook.java:806) 12-16 04:56:59.070: E/AndroidRuntime(822): at com.facebook.android.Facebook.request(Facebook.java:732) 12-16 04:56:59.070: E/AndroidRuntime(822): at com.sara.facebookappl.MainActivity.updateButtonImage(MainActivity.java:83) 12-16 04:56:59.070: E/AndroidRuntime(822): at com.sara.facebookappl.MainActivity.onCreate(MainActivity.java:63) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.Activity.performCreate(Activity.java:5104) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 12-16 04:56:59.070: E/AndroidRuntime(822): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 12-16 04:56:59.070: E/AndroidRuntime(822): ... 11 more 12-16 04:56:59.090: D/dalvikvm(822): GC_CONCURRENT freed 150K, 9% free 2723K/2988K, paused 7ms+58ms, total 239ms

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  • Linq2Sql: query - subquery optimisation

    - by Budda
    I have the following query: IList<InfrStadium> stadiums = (from sector in DbContext.sectors where sector.Type=typeValue select new InfrStadium(sector.TeamId) ).ToList(); and InfrStadium class constructor: private InfrStadium(int teamId) { IList<Sector> teamSectors = (from sector in DbContext.sectors where sector.TeamId==teamId select sector) .ToList<>(); ... work with data } Current implementation perform 1+n queries, where n - number of records fetched the 1st time. I want to optimize that. And another one I would love to do using 'group' operator in way like this: IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IEnumerable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } But attempt to launch query causes the following error: Expression of type 'System.Int32' cannot be used for constructor parameter of type 'System.Collections.Generic.IEnumerable`1[InfrStadiumSector]' Question 1: Could you please explain, what is wrong here, I don't understand why 'team_sectors' is applied as 'System.Int32'? I've tried to change query a little (replace IEnumerable with IQueryeable): IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors.AsQueryable()) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IQueryeable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } In this case I've received another but similar error: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable1[InfrStadiumSector]' of method 'System.Linq.IQueryable1[InfrStadiumSector] AsQueryableInfrStadiumSector' Question 2: Actually, the same question: can't understand at all what is going on here... P.S. I have another to optimize query idea (describe here: Linq2Sql: query optimisation) but I would love to find a solution with 1 request to DB).

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  • Django: Paginator + raw SQL query

    - by Silver Light
    Hello! I'm using Django Paginator everywhere on my website and even wrote a special template tag, to make it more convenient. But now I got to a state, where I need to make a complex custom raw SQL query, that without a LIMIT will return about 100K records. How can I use Django Pagintor with custom query? Simplified example of my problem: My model: class PersonManager(models.Manager): def complicated_list(self): from django.db import connection #Real query is much more complex cursor.execute("""SELECT * FROM `myapp_person`"""); result_list = [] for row in cursor.fetchall(): result_list.append(row[0]); return result_list class Person(models.Model): name = models.CharField(max_length=255); surname = models.CharField(max_length=255); age = models.IntegerField(); objects = PersonManager(); The way I use pagintation with Django ORM: all_objects = Person.objects.all(); paginator = Paginator(all_objects, 10); try: page = int(request.GET.get('page', '1')) except ValueError: page = 1 try: persons = paginator.page(page) except (EmptyPage, InvalidPage): persons = paginator.page(paginator.num_pages) This way, Django get very smart, and adds LIMIT to a query when executing it. But when I use custom manager: all_objects = Person.objects.complicated_list(); all data is selected, and only then python list is sliced, which is VERY slow. How can I make my custom manager behave similar like built in one?

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  • Run Javascript on the body of a Gmail message

    - by saturn
    I want to display LaTeX math in the gmail messages that I receive, so that for example $\mathbb P^2$ would show as a nice formula. Now, there are several Javascripts available (for example, this one, or MathJax which would do the job, I just need to call them at the right time to manipulate the gmail message. I know that this is possible to do in "basic HTML" and "print" views. Is it possible to do in the standard Gmail view? I tried to insert a call to the javascript right before the "canvas_frame" iframe, but that did not work. My suspicion is that manipulating a Gmail message by any Javascript would be a major security flaw (think of all the malicious links one could insert) and that Google does everything to prevent this. And so the answer to my question is probably 'no'. Am I right in this? Of course, it would be very easy for Google to implement viewing of LaTeX and MathML math simply by using MathJax on their servers. I made the corresponding Gmail Lab request, but no answer, and no interest from Google apparently. So, again: is this possible to do without Google's cooperation, on the client side?

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  • jquery .on() toggle div

    - by lollo
    i'm developing a blog with dynamic content loaded via ajax request and i'm trying to hide/show the "post comment" form, of the article, with a button : <div id="post"> ... <ol id="update" class="timeline"> <!-- comments here --> </ol> <button class="mybutton Bhome">Commenta</button><!-- hide/show button --> <div class="mycomment"><!-- div to hide/show --> <form action="#" method="post"> Nome: <input type="text" size="12" id="name" /><br /> Email: <input type="text" size="12" id="email" /><br /> <textarea rows="10" cols="50" class="mytext" id="commentArea"></textarea><br /> <input type="submit" class="Bhome" value=" Post " /> </form> </div><!-- mycomment --> </div><!-- post --> This jquery code works well but has effect on All the posts... $("div").on("click", ".mybutton", function(e){ $(".mycomment").slideToggle("slow"); e.stopPropagation(); }); I want that only the clicked hide/show button has effect on the related article but f i have more than one article on my page the button with .mybutton class hides or shows all the comment form of all the articles.

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  • How to Treat Race Condition of Session in Web Application?

    - by Morgan Cheng
    I was in a ASP.NET application has heavy traffic of AJAX requests. Once a user login our web application, a session is created to store information of this user's state. Currently, our solution to keep session data consistent is quite simple and brutal: each request needs to acquire a exclusive lock before being processed. This works fine for tradition web application. But, when the web application turns to support AJAX, it turns to not efficient. It is quite possible that multiple AJAX requests are sent to server at the same time without reloading the web page. If all AJAX requests are serialized by the exclusive lock, the response is not so quick. Anyway, many AJAX requests that doesn't access same session variables are blocked as well. If we don't have a exclusive lock for each requests, then we need to treat all race condition carefully to avoid dead lock. I'm afraid that would make the code complex and buggy. So, is there any best practice to keep session data consistent and keep code simple and clean?

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  • MySQL LIMIT 1 but query 15 rows?

    - by Ian
    Basically what I'm trying to do is compare the ID's of rows against 15 results in MySQL, eliminating all but 1 (using NOT IN) and then pull that result. Now normally this would be fine by itself, however the order of the 15 rows I'm doing the SQL query for are constantly changing based on a ranking, so there is a possibility that between the time the ranking updates, and the ajax request (which I submit the ID's for NOT IN) more than just one ID has changed, which would of course bring back more than one row which I do not want. So in short, is there a way in which I can query 15 rows, but only return one? Without having to run two separate queries. Any help is appreciated, thank you. EXAMPLE: Say I have 7 items in my database, and I'm displaying 5 on the page to the user. These are what are being displayed to the user: Apple Orange Kiwi Banana Grape But in the database I also have Peach Blackberry Now what I want to do is if the user deletes an item from their list, it will add another item (based on a ranking they have) Now the issue is, in order to know what they have on their list at the moment I send the remaining items to the database (say they deleted Kiwi, I would send Apple, Orange, Banana, and Grape) So now I select the highest ranked 5 items from are remaining six items, make sure they are not the ones already displayed on the page, and then add the new one to list (either Peach or Blackberry) All good and well, except that if both peach and blackberry now outrank grape, then I will be returning two results instead of just one. Because it would've searched... Apple Orange Banana Peach Blackberry and excluded... Apple Orange Banana Grape Which leaves us with both Peach and Blackberry, instead of just Peach or Blackberry

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  • nhibernate mapping: delete collection, insert new collection with old IDs

    - by npeBeg
    my issue lokks similar to this one: (link) but i have one-to-many association: <set name="Fields" cascade="all-delete-orphan" lazy="false" inverse="true"> <key column="[TEMPLATE_ID]"></key> <one-to-many class="MyNamespace.Field, MyLibrary"/> </set> (i also tried to use ) this mapping is for Template object. this one and the Field object has their ID generators set to identity. so when i call session.Update for the Template object it works fine, well, almost: if the Field object has an Id number, UPDATE sql request is called, if the Id is 0, the INSERT is performed. But if i delete a Field object from the collection it has no effect for the Database. I found that if i also call session.Delete for this Field object, everything will be ok, but due to client-server architecture i don't know what to delete. so i decided to delete all the collection elements from the DB and call session.Update with a new collection. and i've got an issue: nhibernate performs the UPDATE operation for the Field objects that has non-zero Id, but they are removed from DB! maybe i should use some other Id generator or smth.. what is the best way to make nhibernate perform "delete all"/"insert all" routine for the collection?

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  • JSF2.0: variable list of custom component

    - by rattaman
    Hello Is there any way of using JSF2.0 in connection with variable lists of components? For example, lets say I have list o people that I would like to edit. They are presented on the page as list of components PersonEditor, which allow changing person data. Each editor is associated with single Person element. In order for this to work I need to perform following steps: On initial request: Get list of people For each person create PersonEditor and associate it with Person object. Fill editor's data. On user action: When user changes values and presses Save, data is processed by backing bean. I can either fill editor with data from list of people or bind it to the backing bean, but not at the same time, so I am stuck. I tried people.xhtml <ui:render value="#{bean.people}" var="person"> <example:personEditor person="#{person}"/> </ui:render> where personEditor.xhtml: a) proper association with person object, but no connection to backing bean <h:form> <h:outputText value="#{cc.attr.person.name}"/> <h:commandButton name="Save" actionListener="editorBean.save"> <f:ajax execute="@form" render="@form"/> </h:commandButton> </h:form> b) no association with person object, but there is connection to backing bean - there is no way to pass that person to the backing bean <h:form> <h:outputText value="#{editorBean.name}"/> <h:commandButton name="Save" actionListener="editorBean.save"> <f:ajax execute="@form" render="@form"/> </h:commandButton> </h:form> If I had each editor on separate page, I could pass the person id as url parameter (either using f:param or f:attribute) and initialize it accordingly. Is there any solution to this problem?

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  • use of ajax in django problem with the code

    - by tazim
    I am new to ajax and using Django for web development. Now My Template contains : sample.html <html> <body> <script language="javascript" type="text/javascript"> //Browser Support Code function ajaxFunction(){ var ajaxRequest; // The variable that makes Ajax possible! try{ // Opera 8.0+, Firefox, Safari ajaxRequest = new XMLHttpRequest(); } catch (e){ // Internet Explorer Browsers try{ ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try{ ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP"); } catch (e){ // Something went wrong alert("Your browser broke!"); return false; } } } // Create a function that will receive data sent from the server ajaxRequest.onreadystatechange = function(){ if(ajaxRequest.readyState == 4){ document.myForm.time.value = ajaxRequest.responseText; } } ajaxRequest.open("GET", "/showtime/", true); ajaxRequest.send(null); } </script> <form name='myForm'> Name: <input type='text' onBlur="ajaxFunction();" name='username' /> <br /> Time: <input type='text' name='time' /> </form> </body> </html> In views.py my function is : def showtime(request): string = "Ajax Application" data = {"string" : string} pprint (data) return render_to_response("sample.html",data) Now, The output is not as expected . The template does not receives the response sent by the server What is wrong with the code ?

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  • Django IntegrityError: foreign key violation upon delete

    - by Lukasz Korzybski
    I have Order and Shipment model. Shipment has a foreign key to Order. class Order(...): ... class Shipment() order = m.ForeignKey('Order') ... Now in one of my views I want do delete order object along with all related objects. So I invoke order.delete(). I have Django 1.0.4, PostgreSQL 8.4 and I use transaction middleware, so whole request is enclosed in single transaction. The problem is that upon order.delete() I get: ... File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 28, in _commit return self.connection.commit() IntegrityError: update or delete on table "main_order" violates foreign key constraint "main_shipment_order_id_fkey" on table "main_shipment" DETAIL: Key (id)=(45) is still referenced from table "main_shipment". I checked in connection.queries that proper queries are executed in proper order. First shipment is deleted, after that django executes delete on order row: {'time': '0.000', 'sql': 'DELETE FROM "main_shipment" WHERE "id" IN (17)'}, {'time': '0.000', 'sql': 'DELETE FROM "main_order" WHERE "id" IN (45)'} Foreign key have ON DELETE NO ACTION (default) and is initially deferred. I don't know why I get foreign key constraint violation. I also tried to register pre_delete signal and manually delete shipment objects before delete on order is called, but it resulted in the same error. I can change ON DELETE behaviour for this key in Postgres but it would be just a hack, I wonder if anyone has a better idea what's going on here. There is also a small detail, my Order model inherits from Cart model, so it actually doesn't have id field but cart_ptr_id and after DELETE on order is executed there is also DELETE on cart, but it seems unrelated? to the shipment-order problem so I simplified it in the example.

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  • Multiple HTTP requests using sockets in java

    - by codeomnitrix
    How could i send multiple http requests from my java program using sockets. actually i have tried as: import java.net.*; import java.io.*; class htmlPageFetch{ public static void main(String[] args){ try{ Socket s = new Socket("127.0.0.1", 80); DataInputStream dIn = new DataInputStream(s.getInputStream()); PrintWriter dOut = new PrintWriter(s.getOutputStream(), true); dOut.println("GET /mytesting/justCheck.html HTTP/1.1\r\nHost:localhost\r\n\r\n"); boolean more_data = true; String str; int i = 0; while(more_data){ str = dIn.readLine(); if(str==null){ //Now server has stopped sending data //So now write again the inputs dOut.println("GET /mytesting/justCheck1.html HTTP/1.1\r\nHost:localhost\r\n\r\n"); continue; } System.out.println(str); } }catch(IOException e){ } } } But when I send the request again it was not processed? Thank in advance.

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  • java url connection, wait for data being sent through the outputstream

    - by Mateu
    I'm writting a java class that tests uploading speed connection to a server. I want to check how many data can be send in 5 seconds. I've written a class which creates a URL, creates a connection, and sends data trough the outPutStream. There is a loop where I writte data to the stream for 5 seconds. However I'm not able to see when data has been send (I writte data to the output stream, but data is not send yet). How can I wait untill data is really sent to the server? Here goes my code (which does not work): URL u = new URL(url) HttpURLConnection uc = (HttpURLConnection) u.openConnection(); uc.setDoOutput(true); uc.setDoInput(true); uc.setUseCaches(false); uc.setDefaultUseCaches(false); uc.setRequestMethod("POST"); uc.setRequestProperty("Content-Type", "application/octet-stream"); uc.connect(); st.start(); // Send the request OutputStream os = uc.getOutputStream(); //This while is incorrect cause it does not wait for data beeing sent while (st.getElapsedTime() < miliSeconds) { os.write(buffer); os.flush(); st.addSize(buffer.length); } os.close(); Thanks

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  • Windows Phone - failing to get a string from a website with login information

    - by jumantyn
    I am new to accessing web services with Windows Phone 7/8. I'm using a WebClient to get a string from a php-website. The site returns a JSON string but at the moment I'm just trying to put it into a TextBox as a normal string just to test if the connection works. The php-page requires an authentication and I think that's where my code is failing. Here's my code: WebClient client = new WebClient(); client.Credentials = new NetworkCredential("myUsername", "myPassword"); client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(client_DownloadStringCompleted); client.DownloadStringAsync(new Uri("https://www.mywebsite.com/ba/php/jsonstuff.php")); void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e) { try { string data = e.Result; this.jsonText.Text = data; } catch (Exception ex) { System.Diagnostics.Debug.WriteLine(ex.Message); } } This returns first a WebException and then a TargetInvocationException. If I replace the Uri with for example "http://www.google.com/index.html" the jsonText TextBox gets filled with html text from Google (oddly enough, this also works even when the WebClient credentials are still set). So is the problem in the setting of the credentials? I couldn't find any good results when searching for guides on how to access php-pages with credentials, only without them. Then I found a short mention somewhere to use the WebClient.Credentials property. But should it work some other way? Update: here's what I can get out of the WebException (sorry for the bad formatting): System.Net.WebException: The remote server returned an error: NotFound. ---System.Net.WebException: The remote server returned an error: NotFound. at System.Net.Browser.ClientHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult) at System.Net.Browser.ClientHttpWebRequest.<c_DisplayClasse.b_d(Object sendState) at System.Net.Browser.AsyncHelper.<c_DisplayClass1.b_0(Object sendState) --- End of inner exception stack trace --- at System.Net.Browser.AsyncHelper.BeginOnUI(SendOrPostCallback beginMethod, Object state) at System.Net.Browser.ClientHttpWebRequest.EndGetResponse(IAsyncResult asyncResult) at System.Net.WebClient.GetWebResponse(WebRequest request, IAsyncResult result) at System.Net.WebClient.DownloadBitsResponseCallback(IAsyncResult result)

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  • Callback from static library

    - by MortenHN
    I think this should be simple, but im having a real hard time finding information about this topic. I have made a static library and have no problem getting the basics to work. But im having a hard time figuring out how to make a call back from the static library to the main APP. I would like my static library to only use one header as front, this header should contain functions like: requestImage:(NSString *)path; requestLikstOfSomething:(NSSting *)guid; and so on.. These functions should do the necessary work and start a async NSURLConnection, and call back to the main application when the call have finished. How do you guys do this, what are the best ways to callback from a static library when a async method is finished? should i do this with delegates (is this possible), notifications, key/value observers. I really want to know how you guys have solved this, and what you regard as the best practices. Im going to have 20-25 different calls so i want the static library header file to be as simple as possible preferable only with a list of the 20-25 functions. UPDATE: My question is not how to use delegate pattern, but witch way is the best to do callbacks from static librarys. I would like to use delegates but i dont want to have 20-25 protocol declarations in the public header file. I would prefer to have only one function for each request. Thanks in advance. Best regards Morten

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  • Strange problems with the Spring RestTemplate in Android application

    - by HarryCater
    I begin to use RESTful api of the Spring Framework in my android client application. But I have encountered with problems when I tried to execute HTTP request via postForObject/postForEntity methods. Here is my code: public String _URL = "https://noticemed.com/app/mobile/login"; public void BeginAuthorization(View view) { HttpHeaders requestHeaders = new HttpHeaders(); requestHeaders.setContentType(MediaType.APPLICATION_JSON); HttpEntity<String> _entity = new HttpEntity<String>(requestHeaders); RestTemplate templ = new RestTemplate(); templ.setRequestFactory(new HttpComponentsClientHttpRequestFactory()); templ.getMessageConverters().add(new MappingJacksonHttpMessageConverter()); ResponseEntity<String> _response = templ.postForEntity(_URL,_entity,String.class); //HERE APP CRASHES String _body = _response.getBody(); And here is a stack trace in logcat after app crashing. As you see there is no definite error message. So the question what am I doing wrong? How to fix this? May there is other way to do it?I really need a help. Thanks in advance!

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  • How to get the compression ratio for a GZipped file ?

    - by Enigma
    Here is how I compressed the data: <%@ page import="javax.servlet.jsp.*,java.io.*,java.util.zip.*" %> <% String encodings = request.getHeader("Accept-Encoding"); PrintWriter outWriter = null; if ((encodings != null) && (encodings.indexOf("gzip") != -1)) { OutputStream outA = response.getOutputStream(); outWriter = new PrintWriter(new GZIPOutputStream(outA), false); response.setHeader("Content-Encoding", "gzip"); int a = response.getBufferSize(); System.out.println("ZIPPED VERSION BF:"+a); } else { System.out.println("UN-ZIPPED VERSION"); outWriter = new PrintWriter(response.getOutputStream(), false); } outWriter.println("<HTML><BODY>"); for(int i=0; i<1000; i++) { outWriter.println(" blah blah blah<br>"); } outWriter.println("</BODY></HTML>"); outWriter.close(); %>

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